PREFACE 



When studying the Warblers some twenty 

 years ago, I became aware of the fact that 

 each male isolates itself at the commencement 

 of the breeding season and exercises dominion 

 over a restricted area of ground. Further in- 

 vestigation, pursued with a view to ascertaining 

 the relation of this particular mode of behaviour 

 to the system of reproduction, led to my studying 

 various species, not only those of close affinity, 

 but those widely remote in the tree of avian 

 life. The present work is the outcome of 

 those investigations. In it I have endeavoured 

 to interpret the prospective value of the be- 

 haviour, and to trace out the relationships in 

 the organic and inorganic world which have 

 determined its survival. Much is mere specu- 

 lation ; much with fuller knowledge may be 

 found to be wrong. But I venture to hope 

 that a nucleus will remain upon which a more 

 complete territorial system may one day be 

 established. 



A2 



